1. Field of the Invention
The present invention relates to a process for producing a semiconductor device, and more particularly to a process for depositing a CVD-SiO.sub.2 film according to a TEOS-O.sub.3 reaction.
2. Prior Art
FIG. 4 is an illustration of a conventional process for depositing a CVD-SiO.sub.2 film according to a TEOS (tetraethyl ortho-silicate, Si(OC.sub.2 H.sub.5).sub.4, an alkoxysilane)-O.sub.3 reaction.
FIG. 4 (a) illustrates a polycrystalline silicon film 6 (hereinafter referred to in brief as a "poly-Si film") formed on a thermal SiO.sub.2 film 4 formed in a surface portion of an Si substrate 2 through a heat treatment thereof. Examples of semiconductor devices including such a structure includes a MOS transistor comprising a gate SiO.sub.2 film coresponding to the thermal SiO.sub.2 film 4 and a gate electrode corresponding to the poly-Si film 6.
On the structure of FIG. 4 (a), a CVD-SiO.sub.2 film 8 is formed as an interlayer insulating film according to the
TEOS-O.sub.3 reaction as shown in FIG. 4 (b).
It has been found out that the surface of the CVD-SiO.sub.2 film 8 in perspective view of FIG. 4 (c), deposited according to the TEOS-O.sub.3 reaction, is even, or smooth, in the areas where the underlying surface is of the poly-Si film 6 (see a partially enlarged view A), but often uneven, or rough, in the areas where the underlying surface is of the thermal SiO.sub.2 film 4 (see a partially enlarged view B).
The data of FIG. 3 obtained through experiment by the inventors of the present invention shows a tendency for the surface roughness of such a CVD-SiO.sub.2 film to increase particularly with an increase in the O.sub.3 concentration in the TEOS-O.sub.3 reaction.
The uneven surface of the CVD-SiO.sub.2 film 8 sometimes causes stress to be put on wirings formed thereon with high liability thereof to undergo disconnection and the like, leading to low reliability of a semiconductor device.
FIG. 3 is a characteristic diagram showing the relationship between the ozone concentration and the
surface state of CVD-SiO.sub.2 film, wherein the abscissa represents the ozone concentration (mol%) while the ordinate represents the surface roughness (.ANG.), which was examined in the experiment by putting and running a probe on a CVD-SiO.sub.2 film to measure a difference of altitude in the up-and-down movement of the probe.
The present invention has been made in view of the foregoing problems of the prior art. Accordingly, an object of the present invention is to provide a process for depositing a CVD-SiO.sub.2 film according to a TEOS-O.sub.3 reaction by which the unevenness of a CVD-SiO.sub.2 film can be suppressed as much as possible.